In capacitive input power devices such as IGBTs (insulated gate bipolar transistors) and MOSFETs (metal oxide semiconductor field effect transistors), when excessive output currents occur during unexpected short circuit conditions, the time to turn off the device must occur over a long enough time interval to minimize any overvoltage which might be caused. This lengthening of the turn off time is necessary because overvoltage is the product of the inductance of the DC (direct current) bus and the di/dt. Therefore if the di/dt is large, the overvoltage will be correspondingly large.
Conventional techniques for responding to excessive device currents include applying a reduced gate voltage with a gate driver stage acting in an analog mode. A limitation of these techniques is that additional circuitry is required for the gate driver, and commercially available gate driver stages experience parasitic effects which prevent proper operation, especially when large power devices (such as, for example, 1000 A/1400 V IGBTs) are used.